#include<stdio.h>

enum LightState{
    RED,YELLOW,GREEN
};

int main(){
    enum LightState LS=RED;

    for(int i=0;i<10;i++){
    switch(LS){
        case RED:
        printf("红灯\n");
        LS=YELLOW;
        break;
        case YELLOW:
        printf("黄灯\n");
        LS=GREEN;
        break;
        case GREEN:
        printf("绿灯\n");
        LS=RED;
        break;
    }
    }


    return 0;
}